Dried chopped onions are one of the best shortcuts you can use to save time in the kitchen. Add these chopped pieces to anything you’re making in a slow cooker or use them to help flavor broth or sauce in long-simmered dishes. To rehydrate, simply soak in warm water for about 15 minutes, then drain. Once they’re rehydrated, they’re a flavorful substitute for fresh onions. Five teaspoons of dehydrated minced onion equals about 1/4 cup rehydrated onion. Ingredients: Onion.